Field of the Invention
The invention relates to a semiconductor component having a semiconductor body of at first conductivity type, that has a doping concentration of more than 5×1013 charge carriers per cm3 and is provided with in each case at least one electrode on two mutually opposite surfaces. At least one of the electrodes makes contact with a semiconductor zone of a second conductivity type opposite to the first conductivity type. The invention relates in particular to an edge structure for such a semiconductor component.
The minimum basic doping of silicon power components is about 8×1012 charge carriers cm−3. In the case of such a basic doping, the bulk reverse voltage of a semiconductor body having a pn junction is of the order of magnitude of 10 kV at room temperature.
In the case of monocrystalline silicon, the intrinsic carrier density at 300° K., that is to say at room temperature, of thermally generated electron-hole pairs is about 1.38×1010 charge carriers cm−3. Such a concentration of the order of magnitude of 1010 charge carriers cm−3 is usually negligible relative to the basic doping of 8×1012 charge carriers cm−3, which is virtually three orders of magnitude higher than the intrinsic charge carrier density.
It should be taken into consideration, however, that the intrinsic density rises exponentially with temperature, with the result that, in the case of a low doping concentration, the intrinsic charge carrier density can increase to a value corresponding to the charge carrier density provided by the basic doping. Thus, by way of an example, an intrinsic density which is reached at a temperature as low as 150° C. (in this case “intrinsic temperature”) corresponds to a basic doping of about 1×1013 charge carriers cm−3. In other words, if the temperature of the semiconductor component lies in the intrinsic range, then the reverse current is drastically increased on account of the thermally generated electron-hole pairs.
These physical specifications inherently restrict the possibilities for using semiconductor components in power engineering, in which voltages of up to 20 kV or more occur. In order nevertheless to be able to control such high voltages, series circuits including a plurality of semiconductor components are used. Moreover, care is taken to ensure that, in the case of semiconductor components having a low basic doping of, for example, less than 1×1013 cm−3 charge carriers in silicon, the maximum operating temperature is not allowed to exceed about 100° C., in order thus to avoid high reverse currents on account of a rising intrinsic density.
European Patent No. EP-B1-0 344 514 discloses a defeatable thyristor having a semiconductor body, which has an n-type emitter layer with an adjoining p-type base layer, a cathodal electrode making contact with the n-type emitter layer, and a p-type emitter layer with an adjoining n-type base layer, an anodal electrode making contact with the p-type emitter layer. The base layers are isolated from one another by a pn junction subject to a reverse-biasing of the thyristor in the blocking state. One of the base layers is provided with a gate electrode to which a turn-off voltage pulse can be fed which causes the thyristor to turn off. At least one semiconductor layer is inserted into the base layer with which the gate electrode does not make contact. This semiconductor layer is not connected to external potentials, runs essentially parallel to the pn junction, is oppositely doped with respect to the base layer and is thin in comparison with the thickness of the semiconductor body. The distance of the semiconductor layer from the pn junction is chosen to be so small so that the maximum field strength of the space charge zone (depletion zone) which builds up at the pn junction when the thyristor is turned off is limited to a value below a critical value which results in an avalanche breakdown with regard to the charge carriers to be depleted in the event of turn-off. The semiconductor layers which are inserted into a base layer and are oppositely doped with respect thereto are provided with continuous cutouts whose dimensions in the lateral direction are small relative to the thickness of the respectively adjoining space charge zones that build up when the thyristor is turned off. In this case, the cutouts may be disposed in such a way as to produce a lattice-shaped structure of the semiconductor layers. The cutouts are intended to improve the ignition behavior of the thyristor.